Low-pressure mercury vapour discharge lamps are commonly used to generate ultraviolet radiation and used to irradiate a fluid to kill potentially harmful organisms contained in the fluid. In mercury-vapour discharge lamps, mercury constitutes the primary component for generating ultraviolet (UV) light. During operation of a low-pressure mercury vapour discharge lamp, the vapour pressure of the mercury greatly affects lamp operation. Commonly, amalgam is used to give off the mercury bonded thereto, thereby controlling the mercury vapour pressure within the so-called amalgam lamp. UV output of the lamp should be as efficient as possible. Therefore, UV transparent bodies need to be used for the production of these lamps. Low-pressure mercury vapour discharge lamps have a tubular lamp body made of quartz.
Conventional high output low-pressure lamps show high surface temperatures. The high temperatures have an unfavourable effect on the amalgam if the lamp is in operation for a long period of time. Often high power load of a lamp causes the amalgam to melt. If the amalgam melts, it may move out of position and could make contact with an electrode and cause possible shorting or ineffective operation of the lamp. In order to overcome this drawback, one option is to use special amalgam mixtures designed to withstand the heat. However, these special amalgam mixtures have a worse efficiency and shorter lifetime compared to standard amalgam mixtures used in standard lamps. Another option is to position the amalgam not too close to the electrode.
DE 10 2013 102 600 A1 discloses a lamp, which consists of a sealed quartz tube with electrodes on each end. The lamp tube contains a small amount of mercury and an inert gas, such as argon or neon, at a low pressure. A quartz tube section of smaller diameter is arranged within an end portion of the quartz tube forming a short section of a concentric double tube with an annular gap, wherein the gap is open towards the inside volume of the lamp. Amalgam is arranged in the annular gap and more precisely attached to the outer surface of the inner concentric tube. This arrangement makes it necessary to join the two concentric tubes at the end portion in a separate manufacturing step.
JP2004-178947A discloses a lamp for lighting purposes. The tubular main body is accordingly made of glass, not of quartz. A neck portion of the glass tube holds a coiled wire with a pitch that is narrower than some mercury allow particles which are thus held inside the coil. The particles are located inside the coil and cannot move inside the lamp, which would lead to damage of the phosphor layer of the lamp.
US2012/0091880A1 discloses another lamp for lighting purposes. The tubular outer housing in made of glass, and the amalgam is enclosed in a cold finger which is provided centrally on one end portion between the electric wires. An indentation of the cold finger prevents the amalgam from being removed from the cold finger. The production of his arrangement is more complex. It is feasible using glass tubes, as in this document. With quartz tubes, as needed for UV radiators, manufacturing seems to be complicated. The working temperature for glass is around 1,000° C., while the working temperature for quartz is above 2,000° C. Also, the temperature range, in which the material can be formed, is significantly narrower than the respective temperature range of glass. Therefore, method of manufacture of glass items cannot be directly adopted for quartz workpieces.